In JP 2009-123550 A, there is disclosed a related-art fuel cell system for controlling a flow rate (actual stack supply flow rate) of a cathode gas supplied to a fuel cell stack to reach a target stack supply flow rate set depending on an electric power request by discharging an unnecessary part of a cathode gas for electric power generation in the fuel cell stack out of the cathode gas discharged from a cathode compressor to a cathode gas discharge passage via a bypass passage.